The present invention relates generally to fiber optic communications, and more specifically to techniques used in connection with wavelength assignment, wavelength filtering, and protection switching in wavelength division multiplexing (WDM) networks.
Photonic transmission, amplification, and switching techniques provide flexible means of provisioning, configuring, and managing modern high capacity telecommunication networks. The physical layer in the network, which includes the transmission equipment and the fiber layer used for signal transport, needs to be reconfigurable in order to support dynamic routing of traffic. While slow reconfiguration (taking on the order of minutes or more) may be sufficient for rearranging traffic capacity in response to change in demand patterns across the network, rapid reconfiguration (perhaps 50 ms or less) is required for restoring services in the case of transmission equipment or fiber cable facility failures. Fast restoration is also critical to prevent escalation of the effects of a single point of failure where the affected services (voice and data) attempt to reconnect immediately following disruption of services and may lead to overloading of facilities adjacent or connected to the point of original failure. With the introduction of multi-wavelength channels in a single fiber, these multi-wavelength channels need to be managed in order to achieve fast restoration.
In addition to the critical need for fast restoration, the capacity that needs to be re-routed has increased rapidly with the continuing increase in data rates for optical transmission and the introduction of multi-wavelength channels on a single fiber. For example, the rapid growth in traffic capacities required for long haul telecommunications networks have accelerated the introduction of new technologies for transmission and multiplexing. Transmission links up to bit rates of 10 Gbps (OC-192) are in commercial service and new developments in multi-wavelength component technologies are resulting in increased commercial availability of 4-, 8-, 16-, 32-, and 40-channel WDM (wavelength division multiplex) links (at 2.5 Gbps per wavelength or more). As the demand for more bandwidth continues, it would be desirable to provide techniques which allow additional multi-wavelength channels with a single fiber to be utilized. Moreover, as the number of multi-wavelength channels within a single fiber increases, it would be desirable to develop techniques to more efficiently multiplex and demultiplex these multi-wavelength channels.
Transmission of high data rates over single fibers also results in making the network more vulnerable to failures of larger magnitude. For example, a single fiber link failure can disrupt approximately 130,000 voice channels (DSO) when the fiber link is operating at 10 Gbps on a single-wavelength or at 2.5 Gbps on each of four wavelengths. Consequently, redundant facilities provisioned for dynamic restoration of service also need to provide a similar magnitude of capacity on the links used as backup or spare links for ensuring network survivability.
Therefore, techniques used in connection with network restoration must provide solutions that are compatible with the twofold requirement of fast switching and high capacity. Various aspects of optical switching in WDM networks are further described in U.S. Pat. No. 6,046,833, the entire disclosure of which, including microfiche appendices, is incorporated by reference in its entirety for all purposes.